There have so far been diverse attempts to more efficiently use different kinds of energies including renewable energies, for example, sunlight and wind power. The renewable energies mostly originating in natural phenomena are very variable in different seasons and different time slots of a day. Due to the fact, unmatched peaks of power demand and power supply is an issue inherently associated with such renewable energies. Large-scale photovoltaic power generation plants need vast laud areas, while wind power plants are well-suited to be built on the oceans or in coastal zones. Such plants are both remote from places where energy consumption actually occurs. Therefore, construction of power cables, which is rather costly, is another issue with renewable energies that needs to be addressed.
To address these issues, energy storage transportation methods and energy carrier systems have been developed and disclosed. A known energy storage transportation method includes steps of producing and storing a hydrogen carrier, such as ammonia, organic hydride, methanol, or dimethylethane, using electric or thermal energy; transporting the produced hydrogen carrier to a power-consuming place; and producing, if necessary, hydrogen from the hydrogen carrier. Hydrogen thus produced in the final step by the energy storage transportation method is utilized for fuel cell-powered vehicles or fuel cell power generation systems as their sources of energy.
The patent document 1 describes a method of producing hydrogen using photovoltaically generated power to actualize such an energy carrier system. The patent document 2 describes a method of synthesizing ammonia from hydrogen and nitrogen. The patent document 3 describes production of hydrogen from ammonia at 400° C. or higher temperatures by using a noble metal catalyst such as Pt, Rh, Pd, or Ru. The methods described in the patent documents 1, 2, and 3 that are combined may enable: conversion of photovoltaically generated power to hydrogen, synthesis of ammonia using the hydrogen as its raw material and storage of the ammonia as liquefied ammonia, transport of the liquefied ammonia to an energy-consuming place, conversion of the liquefied ammonia to hydrogen in the energy-consuming place, and supply of the hydrogen to fuel cell-powered vehicles or fuel cell power generation systems. The total efficiency of conversion of the renewable energy to hydrogen attainable by the combined technical means of the patent documents 1, 2, and 3 is, however, estimated to be not more than approximately 7%. There is a need for an energy carrier system with a higher efficiency of conversion.
The inventors of this invention discussed and developed the techniques to produce hydrogen from one of hydrogen carriers, ammonia, results of which are described in the patent documents 4 and 5. The hydrogen production method described in the patent document 4 irradiates hydrogen source gas containing ammonia gas with ultraviolet including light of a wavelength less than or equal to 200 nm at normal temperature to generate hydrogen gas. The hydrogen production apparatus described in the patent document 5 is equipped with a plasma reactor, a high-voltage electrode, and a grounding electrode. This apparatus produces hydrogen by generating plasma from ammonia through electric discharge between the high-voltage electrode and the grounding electrode at normal temperature and atmospheric pressure. These hydrogen production techniques may afford more efficient production of hydrogen than in the known art, and may be combined with any ammonia production method optimally selected to effectuate an energy storage transportation method and an energy carrier system.